Prostate cancer is the second most fatal cancer among men in the United States, accounting for approximately 28,000 deaths in 2008 (American Cancer Society. Cancer Facts and Figures 2008. Atlanta: American Cancer Society; 2008 2008). Considerable epidemiologic attention in prostate cancer has focused on the vitamin D-endocrine system and on calcium (Schwartz G G. Vitamin D and the epidemiology of prostate cancer. Semin Dial 2005; 18:276-89; Ahn J, Peters U, Albanes D, et al. Serum vitamin D concentration and prostate cancer risk: a nested case-control study. J Natl Cancer Inst 2008; 100:796-804; Tseng M. et al., Dairy, calcium, and vitamin D intakes and prostate cancer risk in the National Health and Nutrition Examination Epidemiologic Follow-up Study cohort. Am J Clin Nutr 2005; 81:1147-54). Although numerous studies have investigated prostate cancer with respect to calcium intake from the diet, the subject of calcium in serum has received scarce attention, perhaps because calcium levels in serum are believed to be under strict homeostatic control. In the only study to specifically address this question, we found an approximately 3-fold increased risk of fatal prostate cancer in the National Health and Nutrition Examination Survey (NHANES I) Epidemiologic Follow Study (NHEFS) for men with total serum levels of calcium in the upper tertile at the baseline exam (Skinner H G, Schwartz G G. Serum calcium and incident and fatal prostate cancer in the National Health and Nutrition Examination Survey. Cancer Epidemiol Biomarkers Prev 2008; 17:2302-5).